The present invention relates to cathode ray tube (CRT) displays, and more particularly to an electronic system for locating the center of deflection of the CRT.
In high resolution display systems, especially in those which project and enlarge images originating on the face of a CRT, precise and accurate alignment of the CRT image center (center of deflection) and the optical axis centerline is essential for satisfactory performance. No method to assure this alignment is in use, alignment typically being based on approximate physical positioning of the CRT using a circular piece of graph paper as a tool. In light of CRT dimensions and imprecision of CRT manufacture, the present method can be quite inaccurate. If the CRT is positioned off-center, the range of deflection correction signal currents may be exceeded and projector alignment become a tedious and inexact process done by hit or miss.
The foregoing method is imprecise, relying on CRT manufacturing deflection center specifications and a questionable tool to make a fundamentally important alignment.
The MM5322 color bar generator chip marketed by National Semiconductor Corporation may be used for NTSC standard television receivers, and generates a number of output test patterns, including a single crosshair. As the chip is understood, its application is limited to a standard television receiver.
It is therefore an object of this invention to provide an apparatus suitable for accurately indicating the vertical and horizontal centers of deflection and deflection axes of any raster-scanned CRT display.